1. Field of the Invention
The present invention relates to microscope systems and objective units used for applications such as the study and imaging of cellular function, and particularly to a microscope system and an objective unit suitable for in-vivo examination of animals, such as mammals.
2. Description of Related Art
Known laser-scanning confocal microscopes include apparatuses for examining cellular function by illuminating the surface of a specimen, such as a living organism, with excitation light to selectively detect fluorescence emitted from a predetermined depth in the specimen, as described on, for example, page 2 of Japanese Unexamined Patent Application Publication No. Hei-3-87804 and FIG. 1 of Japanese Unexamined Patent Application Publication No. Hei-5-72481.
These laser-scanning confocal fluorescence microscopes provide not only a general observation function of microscopes but also a function for acquiring images by scanning a laser beam focused on a minute spot of a specimen with a scanning device, such as a galvano mirror, to detect fluorescence emitted from the specimen.
The laser-scanning confocal microscopes have a resolution high enough to eliminate light other than light from the minute spot of interest, and are therefore advantageous in that they can acquire clear examination images with high S/N ratio.
A method for marking particular molecules, tissues, or cells of a living organism with a dye or fluorescent marker and observing them with a fluorescence microscope or a laser-scanning confocal microscope to examine molecule behavior in the cells or tissues is also known. Because some molecules in individual living organisms of mammals, such as mice, exhibit different behavior from those in cultured cells, it is necessary to examine biological tissues or cells of living organisms while they alive (in vivo). Furthermore, the objective lens of these laser-scanning confocal microscopes is in an infinity system and is constructed such that an image is formed at an imaging lens in the tube barrel (refer to, for example, Japanese Unexamined Patent Application Publication No. Hei-7-306364).
Unfortunately, microscopes including these known laser-scanning confocal microscopes do not assume that various organs of small laboratory animals, such as rats and mice, are examined in vivo. In other words, to observe various organs of a small laboratory animal with a known laser-scanning confocal microscope, it is necessary to cut the skin and muscular tissue or perforate the skull to expose the organs. Furthermore, the size of such an incision or trephination needs to be quite large because the outer diameter of the objective lens to be brought close to the examination site is relatively large.
If this is the case, the small laboratory animal is damaged to such a considerable degree that time-lapse examination over an extended period of time becomes difficult, though observation is possible only for a short period of time after incision or trephination. It would be possible to suture the incision after examination and to cut open the examination site again for another examination at a later time. In general, however, incision itself causes such considerable damage to the small laboratory animal that examination of the animal under normal healthy conditions is difficult.